Sending shared port to application prototype.

Application process started with shared port (and queue) already configured.
But still waits for PORT_ACK message from router to start request processing
(so-called "ready state").

Waiting for router confirmation is necessary.  Otherwise, the application may
produce response and send it to router before the router have the information
about the application process.  This is a subject of further optimizations.

src/nxt_main_process.c

@@ -382,25 +382,25 @@ nxt_main_start_process_handler(nxt_task_t *task, nxt_port_recv_msg_t *msg)
     port = rt->port_by_type[NXT_PROCESS_ROUTER];
     if (nxt_slow_path(port == NULL)) {
         nxt_alert(task, "router port not found");
-        return;
+        goto close_fds;
     }
 
     if (nxt_slow_path(port->pid != nxt_recv_msg_cmsg_pid(msg))) {
         nxt_alert(task, "process %PI cannot start processes",
                   nxt_recv_msg_cmsg_pid(msg));
 
-        return;
+        goto close_fds;
     }
 
     process = nxt_process_new(rt);
     if (nxt_slow_path(process == NULL)) {
-        return;
+        goto close_fds;
     }
 
     process->mem_pool = nxt_mp_create(1024, 128, 256, 32);
     if (process->mem_pool == NULL) {
         nxt_process_use(task, process, -1);
-        return;
+        goto close_fds;
     }
 
     process->parent_port = rt->port_by_type[NXT_PROCESS_MAIN];
@@ -422,6 +422,9 @@ nxt_main_start_process_handler(nxt_task_t *task, nxt_port_recv_msg_t *msg)
         goto failed;
     }
 
+    app_conf->shared_port_fd = msg->fd[0];
+    app_conf->shared_queue_fd = msg->fd[1];
+
     start = b->mem.pos;
 
     app_conf->name.start = start;
@@ -509,6 +512,17 @@ nxt_main_start_process_handler(nxt_task_t *task, nxt_port_recv_msg_t *msg)
 
     ret = nxt_process_start(task, process);
     if (nxt_fast_path(ret == NXT_OK || ret == NXT_AGAIN)) {
+
+        /* Close shared port fds only in main process. */
+        if (ret == NXT_OK) {
+            nxt_fd_close(app_conf->shared_port_fd);
+            nxt_fd_close(app_conf->shared_queue_fd);
+        }
+
+        /* Avoid fds close in caller. */
+        msg->fd[0] = -1;
+        msg->fd[1] = -1;
+
         return;
     }
 
@@ -523,6 +537,14 @@ failed:
         nxt_port_socket_write(task, port, NXT_PORT_MSG_RPC_ERROR,
                               -1, msg->port_msg.stream, 0, NULL);
     }
+
+close_fds:
+
+    nxt_fd_close(msg->fd[0]);
+    msg->fd[0] = -1;
+
+    nxt_fd_close(msg->fd[1]);
+    msg->fd[1] = -1;
 }